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Previous research implies that stereotypic behavior tends to be maintained by the sensory
consequences produced by engaging in the response. Few investigations, however, have focused
on vocal stereotypy. The current study examined the noncommunicative vocalizations of 4
children with an autism spectrum disorder. First, functional analyses were conducted in an
attempt to identify the function of each child?s behavior. For each of the participants, it was
found that vocal stereotypy was likely not maintained by the social consequences. Following
assessment, response interruption and redirection (RIRD) was implemented in an ABAB design
to determine whether vocal stereotypy could be successfully redirected. RIRD involved a teacher
issuing a series of vocal demands the child readily complied with during regular academic
programming. Vocal demands were presented contingent on the occurrence of vocal stereotypy
and were continuously presented until the child complied with three consecutively issued
demands without emitting vocal stereotypy. For each child, RIRD produced levels of vocal
stereotypy substantially lower than those observed in baseline. For 3 of the children, an increase
in appropriate communication was also observed. The children?s teachers were trained to
implement RIRD. Brief follow-up probes and anecdotal information implied that the treatment
had a positive impact in the natural environment.

DESCRIPTORS: vocal stereotypy, automatic reinforcement, response interruption, autism


Stereotypic behavior has been the subject of
intense study for a number of years. Although it
is behavior that occurs during typical develop-
ment (Foster, 1998; Troster, 1994), its persis-
tence in the repertoires of persons with de-
velopmental disabilities is thought to interfere
with skill acquisition (e.g., Dunlap, Dyer, &
Koegel, 1983; Morrison & Rosales-Ruiz, 1997)
and can have adverse social consequences (e.g.,
Jones, Wint, & Ellis, 1990; Wolery, Kirk, &

Gast, 1985). Stereotypic behavior is also among
the diagnostic criteria for autism spectrum
disorders (e.g., Lewis & Bodfish, 1998).
Although it is often also present in persons
with mental retardation, it has been thought
that stereotypy occurs more frequently and at
greater intensities in people with autism (Bod-
fish, Symons, Parker, & Lewis, 2000).

Topographical definitions of stereotypic be-
havior characterize it as repetitive motor and
vocal responses (e.g., Matson, Kiely, & Bam-
burg, 1997; E. A. Smith & Van Houten, 1996).
It is also widely presumed that stereotypy serves
no function (e.g., Bodfish et al., 2000; Matson
et al.), but it has also been postulated that it
might be automatically reinforced by the
sensory consequences that it produces (e.g.,
Iwata, 1999; Lovaas, Newsom, & Hickman,
1987; Rincover, 1978). There is some evidence

We thank Vicki Bousquet, Staci Fitch, Yuko Isono, and
Erin Toomey for their assistance in conducting this study.
Portions of this article were presented at the 28th annual
meeting of the Association for Behavior Analysis, Toronto,
Ontario, May, 2002.

Requests for reprints should be addressed to William H.
Ahearn, New England Center for Children, 33 Turnpike
Road, Southborough, Massachusetts 01772 (e-mail:

doi: 10.1901/jaba.2007.30-06



that stereotypy can be related to demand
situations (Mace, Browder, & Lin, 1987) and
is perhaps sensitive to other social consequences
(e.g., Kennedy, Meyer, Knowles, & Shukla,
2000); however, experimental analyses of ste-
reotypy often indicate that it is either reinforced
by sensory consequences emanating from en-
gaging in the behavior or is controlled by
multiple sources of reinforcement, including the
sensory consequences (Iwata; Kennedy et al.).

Vocal stereotypic behavior has received little
recent study in the behavioral literature.
Schreibman and Carr (1978) describe echolalia
as the ??parroting of the speech of others.?? This
study focused on immediate echolalia, and the
authors developed procedures for replacing the
contextually inappropriate repetitions (or partial
repetitions) of teacher-issued demands by
children with autism with a more appropriate
response (e.g., ??I don?t know?? or a correct
response to the question). Echolalic responses
can also involve vocalizations that do not
involve immediate or near-immediate repeti-
tions of the vocalizations of others or do not
bear a resemblance to words (e.g., Falcomata,
Roane, Hovanetz, Kettering, & Keeney, 2004;
Fay & Schuler, 1980; Lovaas et al., 1987;
Prizant & Rydell, 1984; Taylor, Hoch, &
Weissman, 2005). These vocalizations can vary
in intensity, comprehensibility, and bout
length, and whether they are echos of the
vocalizations of others is often questionable.

One approach to developing treatment for
automatically reinforced behavior has been to
attempt to isolate the specific source of
stimulation that maintains such responding. It
has long been thought that identifying a specific
source of stimulation that maintains a behavior
can be translated into establishing other means
of accessing similar sensory stimulation that can
then be used to reduce undesirable behavior
(e.g., Favell, McGimsey, & Shell, 1982;
Vollmer, 1994). This hypothesis has spurred
productive research that has found that pro-
viding alternative access to the sensory stimu-

lation that maintains behavior (e.g., Goh et al.,
1995; Piazza, Adelinis, Hanley, Goh, & Delia,
2000) can lead to lower levels of stereotypic
behavior. It should be noted that access to
dissimilar forms of sensory stimulation can also
produce lower levels of stereotypy (e.g., Ahearn,
Clark, DeBar, & Florentino, 2005; Vollmer,
Marcus, & LeBlanc, 1994). Furthermore,
Taylor et al. (2005) found that providing
contingent access to matched stimulation
through a negative punishment contingency
(i.e., differential reinforcement of other behav-
ior) produced a low level of vocal stereotypy for
a child with autism, but response-independent
access to that stimulation was ineffective. Such
differential reinforcement is also not always
successful in decreasing stereotypic responding
(e.g., Fellner, Laroche, & Sulzer-Azaroff, 1984).
Fellner et al. found it necessary to include
response blocking with differential reinforce-
ment in a treatment package to produce lower
levels of stereotypy.

As an approach to treating behavior pre-
sumably maintained by sensory stimulation,
response blocking has been referred to as
sensory extinction (Rincover, 1978). Sensory
extinction is typically achieved by either
modifying the environment (e.g., Rincover;
Rincover & Devany, 1982) or directly disrupt-
ing the behavior (e.g., Dorsey, Iwata, Reid, &
Davis, 1982; Reid, Parsons, Phillips, & Green,
1993). However, behavior change achieved
through such procedures can be attributed to
punishment and not extinction (see Lerman &
Iwata, 1996). Moreover, altering the sensory
feedback provided by problem behavior might
be necessary to facilitate an increase in the
probability of other more appropriate behaviors
such as social interaction and cooperative play.

The purpose of the current study was to
systematically assess and treat vocal stereotypy
in children with an autism spectrum disorder.
Initially vocal stereotypy, in children who
exhibited high to moderate levels thought to
interfere with either skill acquisition or social

264 WILLIAM H. AHEARN et al.

acceptance, was exposed to an experimental
analysis to rule out typical social consequences
as a primary maintaining variable (e.g., Iwata et
al., 1994). Response interruption was used in
the current study as an intervention for vocal
stereotypy because response blocking has been
shown to be effective for other forms of
automatically reinforced behavior (e.g., Fisher,
Grace, & Murphy, 1996; Lerman & Iwata,
1996; Reid et al., 1993; R. G. Smith, Russo, &
Le, 1999). In addition, only these four studies
have used response interruption as the sole
means of producing lower levels of problem
behavior (Worsdell, 2000), and none of these
studies involved interruption of vocal responses.
It was assumed that interrupting vocal responses
and redirecting behavior towards appropriate
vocalizations the child had acquired during
instruction (i.e., answering social questions,
vocal imitation) would decrease the probability
of the problem behavior.


Participants and Setting

The participants were 2 boys and 2 girls who
had been diagnosed with an autism spectrum
disorder and had been referred by their clinical
and educational service providers as exhibiting
vocal stereotypy that interfered with their
participation in educational activities or oc-
curred at unacceptable levels outside class. Each
child was receiving intensive vocal and aug-
mentative (except for Mitch, who received only
vocal) communication training prior to and
during the study.

Mitch was a 3-year-old boy who had been
diagnosed with pervasive developmental disor-
der (not otherwise specified) and who received
educational and clinical services in a preschool
setting; he lived with his parents. Although he
initiated communicative attempts inconsistent-
ly, he was able to communicate vocally for the
purposes of requesting specific items and
activities, labeling, rejecting, imitating, greet-
ings, and farewells. In addition, he was able to

answer some social questions (e.g., ??What is
your name???). His vocal stereotypy primarily
consisted of word approximations and noises.
Peter was an 11-year-old boy who had been
diagnosed with autism and who was a residential
student. He also communicated vocally for the
purposes of requesting specific activities and
items, labeling, rejecting, and answering famil-
iar questions, although unintelligible speech was
frequently observed. The majority of his
spontaneous vocalizations were for the purpose
of requesting desired items and rejecting tasks,
but initiation of communicative attempts was
inconsistent. His vocal stereotypy consisted of
a mixture of repeated words, word approxima-
tions, and noises. Nicki and Alice, fraternal
twins, were 7-year-old girls who had been
diagnosed with autism. They were also residen-
tial students at the time the study was
conducted. Nicki?s primary method of commu-
nication was vocal, although she frequently
spoke unintelligibly and initiated communica-
tive attempts inconsistently. The majority of her
spontaneous communication attempts were for
the purposes of requesting desired items. Her
vocal stereotypy consisted of repeated words,
word approximations, and noises. Alice did not
often communicate vocally and rarely initiated
vocally. Her primary mode of communication
was through the use of a picture exchange
communication system (PECS), natural ges-
tures, and some manual signs. The majority of
her spontaneous communicative attempts were
to request desired items. She also readily
participated in vocal imitation exercises. Her
vocal stereotypy primarily consisted of noises
and some word approximations.

All sessions were conducted in a room (1.5 m
by 3 m) equipped with wide-angle video
camera, microphone, video recording equip-
ment, materials necessary to conduct the
experimental conditions, and a table with two
chairs. No materials were included in the rooms
during the treatment comparison that might
confound the effects of the intervention.



Response Measurement and Interobserver

Vocal stereotypy was defined as any instance of
noncontextual or nonfunctional speech and
included singing, babbling, repetitive grunts,
squeals, and phrases unrelated to the present
situation. Examples include ??ee, ee, ee, ee??
outside the context of a vocal imitation task and
laughter in the absence of a humorous event.
Nonexamples include repeating a delivered in-
struction and making or responding to a request.
All functional analysis sessions were 5 min in
duration, and data on vocal stereotypy were
collected using 10-s momentary time sampling.
For every 10 s of session time, an observation of
2 s occurred during which the occurrence or
nonoccurrence of vocal stereotypy was recorded.
The observation moment began as each 10-s
interval elapsed within a session and lasted for
an additional 2 s (e.g., from the 10th through
the 12th second). Momentary time sampling
was used because it provided an efficient and
more accurate estimate of frequency and
duration for stereotypic behavior than partial-
interval recording (Gardenier, MacDonald, &
Green, 2004). Interobserver agreement was
calculated by dividing the number of intervals
with agreements by the total number of
intervals with agreements plus disagreements
and multiplying by 100%. Agreement was
scored for a minimum of 33% (range, 33% to
57%) of each condition for each participant.
Mean total agreement for vocal stereotypy was
95% (range, 91% to 100%) for Mitch, 91%
(range, 86% to 98%) for Peter, 95% (range,
92% to 100%) for Alice, and 94% (range, 87%
to 100%) for Nicki.

Assessment Design, Conditions, and Results

A functional analysis of vocal stereotypy,
based on the procedures reported by Iwata,
Dorsey, Slifer, Bauman, and Richman (1982/
1994), was conducted (see Figure 1). Five-
minute sessions were used because the partici-

pants alternated rapidly between activities in
their educational setting. The demand condi-
tion was modified so that demands were
delivered every 15 s, and 15-s breaks after the
occurrence of vocal stereotypy were delivered.
Demands were those typically encountered
during the child?s instructional programming,
had not been mastered (i.e., performance below
80% correct), and were nonvocal in nature. The
play condition was modified so that response-
independent attention was delivered every 15 s.
The attention and alone conditions were
unmodified, except for session length. Materials
used during the attention and play conditions
were identical, moderately preferred activities
that the child engaged with during assessment.
Immediate echos of the verbal utterances of the
teachers did not result in consequences, were
omitted from the data analyses, and were not
targeted responses. Following the multielement
assessment, a series of alone sessions was
conducted for Mitch, Peter, and Alice. A series
of play sessions was conducted for Nicki
because her vocal stereotypy occurred most
consistently in this condition; however, there
was no response-independent delivery of atten-
tion during this block of sessions. These sessions
were used to determine whether vocal stereoty-
py would persist in the absence of contingent
social consequences. During this phase of the
assessment, three 5-min sessions were con-
ducted each day.

It was found that vocal stereotypy occurred at
the highest level during the alone condition for
both Mitch and Peter. Vocal stereotypy per-
sisted at high levels during the alone-only phase
for Mitch and for Peter after some initial
variability. Alice?s multielement assessment was
undifferentiated, with the lowest level of
behavior observed during the demand condi-
tion. During the alone-only phase, Alice?s vocal
stereotypy was more stable and averaged above
85%. Vocal stereotypy was highly variable
during Nicki?s multielement assessment but
occurred at the highest level in the play

266 WILLIAM H. AHEARN et al.

condition. During the modified play phase,
Nicki?s vocal stereotypy occurred more fre-
quently across each day?s sessions with an
increasing trend across days. The results imply
that vocal stereotypy was not mediated by social
contingencies and was presumably maintained
by the sensory consequences of vocalizing.


Response Measurement and
Interobserver Agreement

During treatment, data on vocal stereotypy
and appropriate vocalizations were collected
using continuous duration recording. Both

vocal stereotypy and appropriate vocalizations
were measured during the baseline and treat-
ment conditions. The definition of vocal
stereotypy was the same as the definition used
during assessment. Appropriate vocalizations
were defined as any contextually appropriate
vocalization not directed by a teacher and
included requests for attention, breaks, or
tangible activities, and comments. An occur-
rence of appropriate vocalization was always
immediately followed by a teacher comment.
Examples of appropriate vocalizations include
requests for social interaction (e.g., ??I want
tickles??), edible items (e.g., ??I want chips??),

Figure 1. Percentage of intervals with stereotypic behavior for Mitch and Peter during multielement sessions and
a series of alone sessions. Percentage of intervals with stereotypic behavior for Alice and Nicki during multielement
sessions and a series of alone sessions for Alice and play without attention sessions for Nicki.


activities (??I want playground??), and comments
(e.g., ??Your shirt is blue??). However, if the
appropriate vocalization occurred twice before
the teacher responded, it was not scored as an
appropriate vocalization. If the vocalization was
repeated following the teacher?s response, it was
scored as another appropriate vocalization.
Nonexamples include repeating a teacher-issued
comment and vocal stereotypy. The total
number of seconds of vocal stereotypy in each
session was divided by the total number of
seconds in the session (300 s) and multiplied by
100% to calculate the proportion of the session
in which stereotypic behavior occurred. Two
independent observers recorded responding for
a minimum of 32% of sessions for each
participant (range, 32% to 45%). Exact agree-
ment (total seconds of vocal stereotypy in
a session recorded by each observer) was
calculated, and agreement exceeded 90% across
conditions and participants. Mean agreement
for vocal stereotypy was 99% (range, 98% to
99%) for Mitch, 90% (range, 84% to 96%) for
Peter, 96% (range, 95% to 98%) for Alice, and
93% (range, 89% to 97%) for Nicki. Data on
appropriate vocalizations were also recorded
continuously. Appropriate vocalizations were
discrete and varied little in duration for all
participants. Cumulative frequency per session
is reported for each participant. Exact agree-
ment was calculated for a minimum of 32% of
each condition for each participant by compar-
ing the cumulative frequencies recorded by
observers; agreement was 100% across condi-
tions and participants.

Response Interruption and Redirection (RIRD)

The effects of response interruption and
redirection (RIRD) were tested in an ABAB
withdrawal design. Baseline sessions were 5 min
in duration and consisted of the student and the
teacher present in the room with a table, chairs,
and no other materials (i.e., no edible items or
activities were present). The purpose was to
systematically apply response blocking and
assess the intervention?s effect on vocal stereo-

typy. Research showing the decelerative effects
of environmental enrichment on behavior and
our clinical experience applying RIRD and
enriched environments led us to question
whether we would be able to identify a treat-
ment effect once we initiated intervention. It
had been anecdotally noted that some children
began to initiate communicative attempts
during RIRD that persisted in the absence of
the treatment and that enriching the environ-
ment sometimes produced more appropriate
responding. This would compromise the de-
termination of functional control over behavior.

If the student independently vocalized, the
teacher delivered praise for using appropriate
language and delivered the request if possible.
For instance, if the student said, ??I want
a tickle,?? the teacher responded by saying,
??Nice job asking for a tickle,?? and briefly
tickled the student. If the child requested an
item (e.g., a chip) that was not available, the
teacher responding by saying, ??Nice job asking
for a chip, maybe we can have some soon.??
There were no programmed consequences for
vocal stereotypy. Baseline continued for at least
three sessions and until vocal stereotypy was
relatively stable or a deteriorating trend was

RIRD was implemented in sessions that
resembled baseline in that the teacher delivered
praise to the student for using appropriate
language and honored requests if possible (no
additional materials were included during
treatment). However, occurrences of vocal
stereotypy were interrupted immediately and
redirection to other vocalizations took place.
For example, the student and teacher were
seated in the room; if the student engaged in
vocal stereotypy, the teacher prompted attend-
ing and then provided prompts for appropriate
language. More specifically, in a neutral tone of
voice the teacher stated the child?s name while
initiating eye contact and issued the prompts
that required a vocal response. The prompts
were in the form of social questions for Mitch,

268 WILLIAM H. AHEARN et al.

Paul, and Nicki (e.g., ??What?s your name???;
??Where do you live???; ??What color is your
shirt???). Vocal imitation (e.g., ??say ball,?? ??say
red,?? ??say dog??) was used for Alice because she
did not reliably answer social questions. For
each child, the vocal demands were skills that
had been performed correctly (i.e., at least 89%
correct per opportunity) and fluently (i.e.,
correct across at least two teachers and settings)
during regular educational instruction. The
teacher continued to provide prompts for
appropriate language until the student complied
with three consecutive correct responses in the
absence of vocal stereotypy, at which time the
teacher delivered social praise for using appro-
priate language (e.g., ??Super job talking!??).
Furthermore, a session clock that started at the
beginning of the session was stopped each time
the teacher implemented RIRD, and was
restarted after the teacher-delivered social praise
following the three consecutive instances of
compliance. The session continued until the
session clock indicated that 5 min had tran-
spired in which the student was not in
treatment. When the treatment sessions were
scored, seconds during which the procedure
was being implemented were subtracted from
the total session time so that each session
consisted of 5 min in which behavior was free
to occur. Neither vocal stereotypy nor appro-
priate vocalizations that occurred during the
RIRD sequence were included in the reported


Training was conducted for each partici-
pant?s teachers. Mitch?s primary teacher served
as the therapist for all of his sessions, and
further training was unnecessary. However, for
the other children, a team of teachers provided
their daily instruction. Therefore, teachers who
worked regularly with the child were provided
training until they reached a high level of
treatment integrity. Teachers also reviewed
videotapes of treatment sessions and were given
written instructions.

For Peter, Alice, and Nicki, pre- and
postintervention probe data were collected.
Prior to the initiation of the functional analysis
and 1 month after the implementation of the
procedures by the child?s teachers in their
classrooms, four videotaped probes were ob-
tained. Each probe was 5 min long and
occurred during naturally occurring demand
and leisure times. Vocal stereotypy was defined
as in assessment and treatment, and was scored
using momentary time sampling as in assess-
ment. Interobserver agreement scores were
obtained in 100% of the pre- and postinterven-
tion probes and exceeded 95% across condi-
tions and children. Data on vocal stereotypy
were also recorded by the student?s clinical team
during regular instructional hours for each
participant. Following the introduction of the
intervention, these data were reviewed for each
child for the remainder of the academic quarters
in their educational plan.


For Mitch, vocal stereotypy occurred at
a moderate to high level, and appropriate
vocalizations occurred infrequently during the
initial baseline (Figure 2). When RIRD was
introduced, vocal stereotypy immediately de-
creased to a low level, and appropriate vocali-
zations occurred more often. During the return
to baseline, vocal stereotypy increased to
a moderate level, and appropriate vocalizations
became slightly less frequent. After the reintro-
duction of RIRD, vocal stereotypy approached
zero, and appropriate vocalizations became
more frequent. For Peter, vocal stereotypy
occurred at a moderate level and appropriate
vocalizations were infrequent during the initial
baseline (Figure 2). When RIRD was intro-
duced, vocal stereotypy decreased to a lower
level, and appropriate vocalizations became
more frequent. During the return to baseline,
a downward trend was obtained for vocal
stereotypy; however, baseline levels were not
recovered. Appropriate vocalizations remained


more frequent than during the initial baseline.
After the reintroduction of RIRD, vocal
stereotypy decreased and appropriate vocaliza-
tions were more frequent. For Alice, vocal
stereotypy occurred at a high level, and
appropriate vocalizations were not observed
during the initial baseline (Figure 3). When
RIRD was introduced, vocal stereotypy de-
creased, and some appropriate vocalizations
were observed. In the return to baseline, vocal
stereotypy increased to a high level, and no
appropriate vocalizations were observed. When
RIRD was reintroduced, vocal stereotypy oc-
curred at a low level, and appropriate vocaliza-
tions became more frequent but were variable.
For Nicki, vocal stereotypy occurred at moder-
ate to high levels during the initial baseline
(Figure 3). When RIRD was introduced, vocal
stereotypy immediately decreased. During the
return to baseline, a moderate level of vocal

stereotypy was observed after several sessions.
When RIRD was reintroduced, a zero level of
occurrence was approached. No appropriate
vocalizations were observed in any of the
conditions for Nicki.


It was also noted that levels of vocal
stereotypy in the natural environment were
substantially lower in the postintervention
probes than in the preintervention probes
(Peter: pretreatment 33% and 44%, posttreat-
ment 1% and 4%; Alice: pretreatment 25% and
77%, posttreatment 3% and 13%; Nicki:
pretreatment 54% and 78%, posttreatment
16% and 24%). Following the intervention,
two to three academic quarters remained in the
educational plans. Each child?s vocal stereotypy
objective was met for each of these quarters,
with the exception of Nicki. For one quarter she

Figure 2. The percentages of each session with stereotypic behavior for Mitch and Peter are depicted on the left axis.
The frequency of appropriate speech is depicted on the right axis.

270 WILLIAM H. AHEARN et al.

made progress on this objective, and the
objective was met for the other two quarters.
Both Mitch and Nicki now receive educational
services in their home school districts.


The present study found that vocal stereotypy
is similar to other forms of stereotypic behavior
in that, at least with these participants, it was
not socially mediated and seemed to be
maintained by its sensory consequences. This
is similar to the findings of Taylor et al. (2005),
which imply that the sounds produced by
stereotypic vocalizations are the operative
sensory consequence that maintains stereotypy.
However, the vibration produced by engaging
in the vocalizations cannot be ruled out as
a reinforcer. Although the assessment data
support this automatic reinforcement hypothe-
sis, stereotypy that persists in the absence of

social contingencies does not rule out sensitivity
to such variables; further research is warranted
towards this end (Vollmer, 1994).

The present study also replicates the findings
of several other studies showing that stereotypic
behavior can be modified by blocking or
interrupting its occurrence (e.g., Fisher et al.,
1996; Lerman & Iwata, 1996; Reid et al., 1993;
R. G. Smith et al., 1999). The current study
replicates the finding that response interruption
alone can produce significant behavior change.
Each of the earlier studies measured the effects
of response blocking with a single participant
(with the exception of Reid et al., in which the
hand mouthing of 2 persons was blocked by
placing a therapist?s hand in front of the client?s
mouth). A unique contribution of this study
was the adaptation of response blocking for
a vocal response.

There are two possible operant mechanisms
for change via this technique. One possibility is

Figure 3. The percentages of each session with stereotypic behavior for Alice and Nicki are depicted on the left axis.
The frequency of appropriate speech is depicted on the right axis.


that the sensory consequences of vocal stereo-
typy were dampened by response interruption,
and stereotypy was extinguished. This is
consistent with the assertions of Rincover
(1978) and Reid et al. (1993). However, the
only empirical demonstration that response
blocking produces change through extinction
is provided by R. G. Smith et al. (1999). After
demonstrating that response blocking effectively
reduced behavior, Smith et al. blocked some but
not all responses, varying the proportion of
responses blocked systematically. It was not
until nearly all responses had been blocked that
behavior became less frequent, indicating that
behavior changed through extinction. Alterna-
tively, response blocking may serve as an
aversive event contingently produced by behav-
ior. Lerman and Iwata (1996) demonstrated
that punishment was the operative mechanism
of change when they systematically blocked
some but not all responses. The current study
was not, however, designed to distinguish
between these possible mechanisms. Future
research that arranges for systematically block-
ing proportions of responses as in Lerman and
Iwata and Smith et al. across a large number of
participants would be necessary to identify the
most likely operant mechanism for response
blocking. As these studies suggest, the mecha-
nism may be idiosyncratic.

In addition, the decreased occurrence of vocal
stereotypy may have established the conse-
quences for appropriate speech as more reinfor-
cing for the 3 children who spoke more during
the RIRD condition. Recall that there was no
difference in the contingencies for appropriate
speech across baseline and treatment. That
appropriate vocalizations emerged was a positive
side effect of RIRD. Teachers were directed to
respond to appropriate speech in a manner
analogous to how the speech would be
responded to in the natural environment. That
is, teachers praised the use of appropriate speech
and honored those requests that could be
accommodated. Having arranged specific or

incidental instruction to emit appropriate
vocalizations (e.g., requests or comments)
would have potentially augmented the treat-
ment effects but could have interfered with
establishing functional control by the treatment
over responding. This study was arranged to
specifically test the effects of response blocking,
and future investigations should test the effects
of arranging specific instruction for appropriate
vocal behavior (e.g., mand or tact training or
baiting the environment with preferred stimuli)
in combination with response interruption.
That appropriate vocalizations did not emerge
for Nicki, who was more verbally competent
than Alice, w

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